1. Field of the Invention
The present invention relates to a reflection type liquid crystal display.
2. Description of the Related Art
A number of reflection type liquid crystal displays that create a recognizable image by reflecting incident light originating from the observer""s side have been proposed to date.
FIG. 1 is a sectional view of one such conventional reflection type liquid crystal display.
As shown in FIG. 1, such a conventional reflection type liquid crystal display has a thin film transistor (hereinafter referred to as the TFT) as a switching element on an insulating substrate 10 of quartz glass or non-alkali glass or the like.
First, gate electrodes 11 of a refractory metal, such as chromium (Cr) or molybdenum (Mo), a gate insulating film 12, and active layers 13 of polysilicon films are successively formed on the insulating substrate (TFT substrate) 10.
Each active layer 13 includes channels 13c formed above the gate electrodes 11, and a source 13s and a drain 13d that are formed on both sides of the channels 13c by ion doping using stopper insulating films 14 on the channels 13c as masks.
Then, an inter-layer insulating film 15, which includes a SiO2 film, a SiN film and a SiO2 film deposited in succession, is formed over the entire surfaces of the gate insulating film 12, the active layer 13 and the stopper insulating films 14. A drain electrode 16 is formed by filling a contact hole, which is formed to correspond to the drain 13d, with a metal, such as aluminum (Al). Furthermore, a planarization insulating film 17, which consists of an organic resin, for example, and serves to flatten the surface, is formed over the entire surface. A contact hole is formed at a location of the planarization insulating film 17 corresponding to the source 13s. A reflective display electrode 19 as a reflection electrode, which consists of aluminum (Al) in contact with the source 13s through this contact hole and serves also as the source electrode 18, is formed on the planarization insulating film 17. An alignment film 20 consisting of an organic resin, such as polyimide, and aligning liquid crystal elements 21, is formed on the reflective display electrode 19.
On a counter electrode substrate 30 facing the TFT substrate 10 and comprising an insulating substrate, are provided a color filter 31 including primary colors, red (R), green (G), and blue (B) and a black matrix 32 with a function to shield light; a protective film 33 of a resin formed on the color filter 31; and a counter electrode 34 and an alignment film 35 formed over the entire surface of the protective film 33. On the side not facing the TFT substrate 10, a polarizer 41 is located. The counter electrode substrate 30 and the TFT substrate 10 are bonded together with their peripheries sealed with a sealing bond (not shown), thus forming a space inside, and this space is filled with a twisted nematic (TN) liquid crystal 21.
The propagation of light when a user views the reflection type liquid crystal display as above is described below with reference to FIG. 1.
As indicated by a broken line, a natural light 100 coming from the outside enters from the polarizer 41 on the side of an observer 101, and passes through the counter electrode substrate 30, the color filter 31, the protective film 33, the counter electrode 34, the alignment film 35, the alignment film 20, the TN liquid crystal 21, and the alignment film 20 on the TFT substrate 10. The light is reflected by the reflective display electrode 19, travels through the layers in a direction opposite to the direction of incidence, emerges from the polarizer 41 on the counter electrode substrate 30 and enters the eyes of the observer 101.
However, when, as indicated by broken line 102, the incident natural light advances linearly and is reflected by the reflective display electrode 19 of the reflective material, the reflected light travels linearly and in parallel with the light 100. Therefore, a part of the light 102 travelling linearly in parallel travels through a place not related with a display, such as the black matrix 32 of the color filter 31.
Therefore, when the display is observed, the observed display in a specific viewing angle can be bright by the light having passed through a place other than the place not related with the display, but the entire observed image is disadvantageously dark. Moreover, as another disadvantage, an image blur, or a bleeding of a color image tends to be easily generated because the light of a pixel to be displayed is emitted from other pixels in the vicinity as shown in FIG. 1.
The present invention has been made to rectify the disadvantages described above and has as its object to provide a reflection type liquid crystal display that enhances a luminance of each display pixel and offers a high-quality display.
According to one aspect of the present invention, there is provided a reflection type liquid crystal display, which comprises a liquid crystal held in a gap between a first substrate and a second substrate disposed facing each other, and electrodes for driving the liquid crystal for each pixel disposed on the first and second substrates facing the liquid crystal. The electrode on the first substrate comprises a plurality of reflective display electrodes divided for the pixels and formed of conductive reflective materials, and each of the plurality of reflective display electrodes has a concavity toward the first substrate on at least a surface facing the liquid crystal.
According to another aspect of the present invention, in the reflection type liquid crystal display, a switching element for each pixel is further formed on the first substrate, and the switching element is connected to the corresponding electrode out of the plurality of reflective display electrodes.
According to yet another aspect of the present invention, at least a surface of the reflective display electrode facing the liquid crystal is concaved toward the first substrate in the vicinity of a pixel area center.
As described above, since the reflective display electrode is provided with the concavity in each pixel area, the light reflected by the reflective display electrode is converged within the pixel area, so that the light is prevented from being propagated or lost through a light shield area other than the pixel area as an invalid light, or from being emitted from an adjacent pixel area. Therefore, the luminance of the reflected light obtained in each display pixel can substantially be enhanced. Moreover, since the reflected light is emitted from the same pixel area without leaking to adjacent pixels, image blur and the bleeding of a displayed color image can be prevented, so that a display quality can be enhanced.
Furthermore, in the present invention, the second substrate is provided with a light diffusing member, so that the light converged by the concavity of the reflective display electrode can be diffused and emitted. Therefore, the intensity of the emitted light can be uniformed in a single pixel, luminance nonuniformity is prevented and the display quality can further be enhanced.
In still another aspect of the present invention, the concavity of the reflective display electrode may also be obtained by the following constitution.
For example, in the device, at least an insulating film is formed between the reflective display electrode and the first substrate.
A concavity toward the first substrate is formed on the surface of the insulating film facing the liquid crystal for each of the pixel areas. The concavity of the insulating film is continued to the surface of the reflective display electrode facing the liquid crystal, formed on the insulating film.
Moreover, the switching element formed for each pixel and a wire for supplying a signal to the switching element are formed on the first substrate. The plurality of reflective display electrodes are formed on the insulating film which is formed on the whole surface of the substrate so as to cover the switching element and the wire. Each of the plurality of reflective display electrodes is positioned so as to cover rising areas disposed by the provision of the corresponding switching element and/or the wire on the surface of the insulating film and a concaved area held between the rising areas, and irregularities of the surface of the insulating film are continued to the surface of the reflective display electrode facing the liquid crystal.
According to yet another aspect of the present invention, there is provided a reflection type liquid crystal display, which comprises a liquid crystal held in a gap between a first substrate and a second substrate disposed facing each other; and electrodes for driving the liquid crystal disposed on the first and second substrates facing the liquid crystal. The electrode formed on one of the first and second substrates is a reflective display electrode formed of a conductive reflective material, and at least a surface of the reflective display electrode facing the liquid crystal has a concavity toward the substrate in each pixel area.
According to still another aspect of the present invention, there is provided a method of manufacturing a reflection type liquid crystal display provided with a liquid crystal held in a gap between a first substrate and a second substrate disposed facing each other, and electrodes for driving the liquid crystal formed on the first and second substrates facing the liquid crystal, said method comprising the steps of forming a reflective display electrode with a conductive reflective material on the first substrate and of selectively etching the surface of the reflective display electrode to form a concavity toward the first substrate on the surface of the reflective display electrode.
According to still another aspect of the present invention, there is provided a method of manufacturing a reflection type liquid crystal display provided with a liquid crystal held in a gap between a first substrate and a second substrate disposed facing each other, and electrodes for driving the liquid crystal formed on the first and second substrates facing the liquid crystal, said method comprising the steps of forming an insulating film on the first substrate; selectively etching the surface of the insulating film to form a concavity toward the first substrate for each pixel area on the surface of the insulating film; and forming a reflective display electrode with a conductive reflective material on the insulating film.
As described above, according to the present invention, a reflection type liquid crystal display can be obtained, in which the luminance of each display pixel is enhanced, and a bright image can be displayed in a wider viewing angle.